enhance: Allow external sources to overwrite components and extensions

this is like the themes now . If some component/extension found in
both lualine repo and in some other rtp path then the one outside
the repo will be loaded.
+ Added better error handling for extensions.

lua/lualine/utils/loader.lua

@@ -1,23 +1,81 @@
 -- Copyright (c) 2020-2021 hoob3rt
 -- MIT license, see LICENSE for more details.
+local notice = require'lualine.utils.notices'
+
+local function lualine_load(patern, use_cache)
+  local retval, cache_name = nil, nil
+  local sep = package.config:sub(1,1)
+
+  if use_cache == true then
+    -- Turn {lua, lualine, module, name} -> lualine.module.name
+    -- same formst that require uses
+    -- then check if it's in requires cache
+    local copy_patern = {}
+    local start = patern[1] == 'lua' and 2 or 1
+    local copy_start = 1
+    for i=start, #patern do
+      copy_patern[copy_start] = patern[i]
+      copy_start = copy_start + 1
+    end
+    cache_name = table.concat(copy_patern, '.')
+    if package.loaded[cache_name] then
+      return package.loaded[cache_name]
+    end
+  end
+
+  -- Get all the runtime files that match the patern
+  local files = vim.fn.uniq(vim.api.nvim_get_runtime_file(
+                  table.concat(patern, sep)..'.lua', true))
+  local n_files = #files
+
+  if n_files == 0 then
+    -- No match found
+    error(table.concat(patern, sep) .. " Not found")
+  elseif n_files == 1 then
+    -- when only one is found run that and return it's return value
+    retval =  dofile(files[1])
+  else
+    -- More then 1 found . Use the first one that isn't in lualines repo
+    local lualine_repo_pattern = table.concat({'lualine.nvim', 'lua', 'lualine'}, sep)
+    local file_found = false
+    for _, file in ipairs(files) do
+      if not file:find(lualine_repo_pattern) then
+        retval = dofile(file)
+        file_found = true
+        break
+      end
+    end
+    if not file_found then
+      -- This shouldn't happen but somehow we have multiple files but they
+      -- apear to be in lualines repo . Just run the first one
+      retval =  dofile(files[1])
+    end
+  end
+
+  if use_cache == true and cache_name then
+    package.loaded[cache_name] = retval
+  end
+  return retval
+end
+
 local function component_loader(component)
   if type(component[1]) == 'function' then
     return
-        require 'lualine.components.special.function_component':new(component)
+      lualine_load({'lua', 'lualine', 'components', 'special', 'function_component'}, true):new(component)
   end
   if type(component[1]) == 'string' then
     -- load the component
-    local ok, loaded_component = pcall(require,
-                                       'lualine.components.' .. component[1])
+    local ok, loaded_component = pcall(lualine_load,
+                          {'lua', 'lualine', 'components', component[1]}, true)
     if ok then
       component.component_name = component[1]
       loaded_component = loaded_component:new(component)
     elseif component[1]:find('[gvtwb]?o?:') == 1 then
       loaded_component =
-          require 'lualine.components.special.vim_var_component':new(component)
+        lualine_load({'lua', 'lualine', 'components', 'special', 'vim_var_component'}, true):new(component)
     else
       loaded_component =
-          require 'lualine.components.special.eval_func_component':new(component)
+        lualine_load({'lua', 'lualine', 'components', 'special', 'eval_func_component'}, true):new(component)
     end
     return loaded_component
   end
@@ -45,9 +103,12 @@ local function load_components(config)
 end
 
 local function load_extensions(config)
-  for index, extension in pairs(config.extensions) do
+  local loaded_extensions = {}
+  for _, extension in pairs(config.extensions) do
     if type(extension) == 'string' then
-      local local_extension = vim.deepcopy(require('lualine.extensions.' .. extension))
+      local ok, local_extension = pcall(lualine_load, {'lua', 'lualine', 'extensions', extension}, true)
+      if ok then
+        local_extension = vim.deepcopy(local_extension)
         load_sections(local_extension.sections, config.options)
         if local_extension.inactive_sections then
           load_sections(local_extension.inactive_sections, config.options)
@@ -55,7 +116,13 @@ local function load_extensions(config)
         if type(local_extension.init) == 'function' then
           local_extension.init()
         end
-      config.extensions[index] = local_extension
+        table.insert(loaded_extensions, local_extension)
+      else
+        notice.add_notice(string.format([[
+### Extensions
+Extension named `%s` was not found . Check if spelling is correct.
+]], extension))
+      end
     elseif type(extension) == 'table' then
       local local_extension = vim.deepcopy(extension)
       load_sections(local_extension.sections, config.options)
@@ -65,9 +132,10 @@ local function load_extensions(config)
       if type(local_extension.init) == 'function' then
         local_extension.init()
       end
-      config.extensions[index] = local_extension
+      table.insert(loaded_extensions, local_extension)
     end
   end
+  config.extensions = loaded_extensions
 end
 
 local function load_all(config)
@@ -75,21 +143,8 @@ local function load_all(config)
   load_extensions(config)
 end
 
-local function load(patern)
-  local files = vim.fn.uniq(vim.api.nvim_get_runtime_file(patern, true))
-  local n_files = #files
-  if n_files == 0 then return nil
-  elseif n_files == 1 then return  dofile(files[1])
-  else
-    for _, file in ipairs(files) do
-      if not file:find('lualine.nvim') then return dofile(file) end
-    end
-  end
-end
-
 local function load_theme(theme_name)
-  return load(table.concat(
-               {'lua', 'lualine', 'themes', theme_name..'.lua'}, package.config:sub(1, 1)))
+  return lualine_load({'lua', 'lualine', 'themes', theme_name}, false)
 end
 
 return {